1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magneto-resistive material as a function of the amount and direction of magnetic flux being sensed by the element.
The prior art also teaches that in order for an MR element to operate optimally, two bias field should be provided. In order to bias the material so that its response to a flux field is linear a transverse bias field is generally provided. This bias field is normal to the plane of the magnetic media and parallel to the surface of the planar MR element.
The other bias field which is usually employed with MR elements is referred to in the art as the longitudinal bias field which extends parallel to the surface of the magnetic media and parallel to the lengthwise direction of the MR element. The function of the longitudinal bias field is to suppress Barkhausen noise which originates from multi-domain activities in the MR element.
Numerous prior art biasing methods and apparatus for MR sensors have been developed which use both longitudinal and transverse bias together, and these prior art biasing methods and apparatus have been effective to meet prior art requirements. However, the drive toward increased recording density has led to the requirement for narrower recording tracks and increased linear recording density along the tracks. The small MR sensors which are necessary to meet these requirements cannot be made with the use of the prior art techniques due to competing bias requirements. On the one hand, the longitudinal bias must be strong enough for domain suppression and this bias produces a field along the MR element. On the other hand, the transverse bias field is normal to the longitudinal bias field, so the longitudinal bias field competes against the transverse bias field and the transverse data signal. As a result of this bias competition, the MR sensor is chronically underbiased and signal sensitivity is significantly reduced. These high recording density applications require a very efficient output which prior art techniques are unable to produce.
Commonly assigned U.S. Pat. No. 3 887,944 discloses an integrated array of side-by-side MR reading heads. To eliminate crosstalk between adjacent MR read heads, a region of high coercivity material is formed between adjacent MR sensors. One of the ways discussed to produce the region of high coercivity material is by exchange coupling between an antiferromagnetic material and the MR sensor. However, there is no consideration of the possibility of obtaining exchange bias fields from this coupling, the direction of such bias fields, if they do exist, and the subsequent domain states of the MR sensor.
Commonly assigned U.S. Pat. No. 4,103,315 discloses the use of antiferromagnetic-ferromagne exchange coupling to produce a uniform longitudinal bias along the entire MR sensor for domain suppression.
The prior art does not disclose a MR sensor which is biased with longitudinal bias only in the end regions and transverse bias in a central active region, where actual sensing of data is accomplished.